1. Field of the Invention
The present invention relates to a general-purpose methodology for extracting and rendering data from digital charting databases and, more particularly, to a method for integrating and combining bathymetric/topographic data from several sources operating on ordinary desktop personal computers.
2. Description of the Prior Art
A necessary prerequisite to display a 3-dimensional (3-D) tactical picture is the ability to access bottom/terrain data and render those data in real time. For example, any submarine-based tactical system must access information from the submarine's combat control system (CCS) databases. An onboard bathymetry database used in support of the Common Tactical Picture (CTP) is the NIMA product Digital Nautical Chart (DNC). The DNC is an unclassified, vector-based digital database containing maritime features essential for safe marine navigation. The database consists of a portfolio of approximately 5000 nautical charts that provide global marine navigation between 84° North latitude and 81° South latitude and supports a variety of Geographic Information System (GIS) applications. NIMA has produced the DNC to support worldwide navigation requirements of the U.S. Navy and U.S. Coast Guard.
In addition to bathymetry the DNC database contains nautical features consisting of points, lines, and polygons. These features have been collected individually and assembled to support its use by GIS and other scientific applications.
The size of both modeled and measured data in the DNC database presents a challenge to computer's ability to extract the data and visualize it at interactive speed. Older methods of visualization relied on heavy post-processing of the data into image files that could be played back as movies or plotted and studied for future use. These methods were slow and failed to fully exploit the information value of the data. There are varied efforts underway to progress toward interactive visualization. For example, tools exist for comparing multivariate data sets to imagery data sets in both geographic and multivariate feature space. An example tool supports various input data formats, allows visualization in three data spaces, active querying with text output in two data spaces, selection of areas, and manual classification in two data spaces. Still, graphics systems of mid-end workstations often cannot render the geometry fast enough to be interactive.
U.S. Pat. No. 6,515,663 to Hung et al. describes a method and apparatus for the efficient rendering of a three-dimensional object on a flat screen in stereo 3-D such that the left and right eyes can view two different images (i.e. the same object from slightly different viewpoints), making the image appear to extend out of the screen and into real three-dimensional space.
U.S. Pat. No. 6,556,194 to Shiono describes a method of combining partial descriptions of a three-dimensional object, obtained from different perspectives, and merging that data into a single, complete description of that object, valid from all perspectives. The method defines shape vectors using ranges and directions from the surface points. The various sets of shape vectors from differing perspectives are then merged through vector arithmetic, yielding a single, unified shape vector description of the object.
U.S. Pat. No. 6,563,500 to Kim et al describes a method and apparatus for the efficient coding and decoding of a 3-D triangle mesh dataset for the purpose of transmission. The method attempts to speed transmission by coding to allow the receiving end to begin mesh reconstruction before the entire dataset is received, and also allowing partial reconstruction even if there is lost data. The method basically consists of taking a complete 3-D mesh dataset, splitting it into chunks, encoding it, sending it, receiving it, decoding it, and recombining it. The mesh is split along natural “fault lines” as opposed to arbitrary division lines, chosen to make the pieces regular in size and shape.
U.S. Pat. No. 6,606,089 to Margadant describes a method of visualizing spatially resolved data by means of a superposition of texture maps. The method involves taking sampled three-dimensional data, loading it as texture maps (a two-dimensional surface that is “wrapped around” a three-dimensional object, giving the 3-D object a surface texture similar to that of the 2-D surface, analogous to applying wallpaper, paint, or veneer to a real object, and then allowing the graphics rendering hardware to superpose these maps to rapidly create a pictorial representation of the data). The method avoids rendering a complete mesh description of the object and instead rapidly generates pictures of the data.
None of the foregoing approaches are well-suited for DNC data which requires “direct read” software that provides for display without data manipulation. The present invention finds that “direct read” is possible by extraction of all information (including both navigational and bathymetric information) generated from the DNC database, and generating a three-dimensional triangle mesh description of sampled data. The present system as will be disclosed integrates and combines bathymetric/topographic data from several sources operating on ordinary desktop personal computers, saving development time and associated expenses in addition to providing for widespread portability.